1. Field of the Invention
The present invention relates to nanohole structures adapted to magnetic recording media, and method for economically and efficiently producing the nanohole structures; stampers properly utilized to produce the nanohole structures and capable of producing the nanohole structures efficiently, and methods for producing the stampers; magnetic recording media adapted to hard disks utilized in various products such as external memory devices of computers and recording devices of public videos, capable of easy tracking, and allowing high-density recording, high-speed recording, and higher capacity, and methods economically and efficiently for producing the magnetic recording media; and magnetic recording devices and magnetic recording methods that utilize the magnetic recording media in perpendicular recording manner.
2. Description of the Related Art
With technological innovations in information technology industries, demands have been made to provide magnetic recording media which have larger capacity, enable high-speed recording, and are available at lower cost. In order to attain the larger capacity, high-speed recording, and lower cost, the recording density is essentially required to increase in the magnetic recording media. Previously, recording densities of magnetic recording media have been increased by horizontally recording information on continuous magnetic films in the media. However, the related technology may almost have saturated; namely, when crystal grains of magnetic particles constituting the continuous magnetic film have large sizes, complex magnetic domains are formed to thereby increase noise. In contrast, when the magnetic particles have smaller sizes to avoid the noise, the magnetization tends to decrease with time due to thermalfluctuation, thus inviting errors. In addition, demagnetizing field for recording relatively increases with increasing recording densities of magnetic recording media. Thus, the magnetic recording media must have an increased coercive force and do not have sufficient overwrite properties due to insufficient writing ability of recording heads.
Recently, considerable efforts have been made to develop an advanced recording system in place of the horizontal recording systems. One of them is a recording system using a patterned magnetic recording medium, in which a magnetic film in the medium is not a continuous film but is in the pattern of, for example, dot, bar or pillar on the order of nanometers and thereby constitutes not a complex magnetic domain structure but a single domain structure (e.g., S. Y. Chou Proc. IEEE 85 (4), 652 (1997)). Another is a perpendicular recording system, in which a recording demagnetization field is smaller and information can be recorded at a higher density than in the horizontal recording system, the recording layer can have a somewhat large thickness and the recording magnetization is resistant to thermalfluctuations (e.g., Japanese Patent Application Laid-Open (JP-A) No. 06-180834). On the perpendicular recording system, JP-A No. 52-134706 proposes a combination use of a soft-magnetic film and a perpendicularly magnetized film. However, this proposal is insufficient in writing ability with a single pole head. To avoid this problem, JP-A No. 2001-283419 proposes a magnetic recording medium further comprising a soft-magnetic underlayer. Such magnetic recording on a magnetic recording medium according to the perpendicular recording system is illustrated in FIG. 1. A read-write head of single pole head 100 of perpendicular-magnetic-recording system has main pole 102 facing recording layer 30 of the magnetic recording medium. The magnetic recording medium comprises a substrate, soft-magnetic layer 10, intermediate layer 20 (nonmagnetic layer) and a recording layer 30 (perpendicularly magnetized film) arranged in this order. The main pole 102 of the read-write head 100 (single pole head) supplies a recording magnetic field toward the recording layer 30 (perpendicularly magnetized film) at a high magnetic flux density. The recording magnetic field flows from the recording layer 30 (perpendicularly magnetized film) via the soft-magnetic layer 10 to latter half portion 104 of the read-write head 100 to form a magnetic circuit. The latter half portion 104 has a portion facing the recording layer 30 (perpendicularly magnetized film) with a large size, and thereby its magnetization does not affect the recording layer 30 (perpendicularly magnetized film). The soft-magnetic layer 10 in the magnetic recording medium also has the same function as the read-write head 100 (single pole head).
However, the soft-magnetic layer 10 focuses not only the recording magnetic field supplied from the read-write head 100 (single pole head) but also a floating magnetic field leaked from surroundings to the recording layer 30 (perpendicularly magnetized film) to thereby magnetize the same, thus inviting increased noise in recording. The patterned magnetic film requires complicated patterning procedures and thus is expensive. In the magnetic recording medium having the soft-magnetic underlayer, the soft-magnetic underlayer must be arranged at a close distance from the single pole head in magnetic recording. Otherwise, a magnetic flux extending from the read-write head 100 (single pole head) to the soft-magnetic underlayer 40 diverge with an increasing distance between the two components, and information is recorded in a broadened magnetic field with larger bits in the lower part of the recording layer 30 (perpendicularly magnetized film) arranged on the soft-magnetic underlayer 40 (see FIGS. 2A and 2B). In this case, the read-write head 100 (single pole head) must supply an increasing write current. In addition, if a small bit is recorded after recording a large bit, a large portion of the large bit remains unerased, thus deteriorating the overwrite properties.
As such, advanced magnetic recording media are proposed that combines perpendicular recording in addition to the recording on the base of patterned media and comprises a magnetic metal inserted within pores of anodizing alumina pores (e.g. JP-A No. 2002-175621).
As shown in FIG. 3, the magnetic recording medium comprises anodized alumina pores 130 (alumina layer), underlayer electrode 120 on substrate 110 in this order. Many alumina pores are arranged in a pattern at the anodized alumina pores 130 (alumina layer), and a ferromagnetic metal is inserted within the alumina pores to form ferromagnetic layer 140.
In the magnetic recording medium comprising the anodized alumina pores inserted with a magnetic material, the anodized alumina pores extend with a high aspect ratio in a direction perpendicular to an exposed surface. The medium is susceptible to magnetization in the perpendicular direction, is dimensionally anisotropic with respect to the magnetic material, and is resistant to thermalfluctuation. The anodized alumina pores generally grow in a self-organizing manner to form honeycomb lattices of hexagonal closest packing and can be produced at lower cost than in the formation of such pores one by one by lithography processes. The patterns for acting as origins of alumina pores may beneficially make possible to form magnetic arrays having optional array patterns.
The methods for forming a pattern of alumina pore origins are exemplified by pattern forming methods by use of photolithography processes and by use of stampers to press a pattern, which are demanded to form patterns economically and efficiently. Methods on the concept of arranging fine particles have been expected for application to methods for forming surface configuration of stampers. The methods on the concept of arranging fine particles may lead to a method to form a hexagonal close-packed pattern by use of self-organization through arranging nano-fine particles with a desirable pitch and a size on a flat substrate. The methods on the concept of arranging fine particles may be based on pulling out processes or centrifugal processes. The centrifugal processes are related to the method in which a substrate is immersed into a dispersion of fine particles and the substrate and the dispersion are centrifuged to press the fine particle onto the substrate by action of centrifugal force, thereby closest packing of monolayer fine particles is obtainable (see JP-A No. 2003-226984), which are advantageous in that the process is simple and easy and the processing period is relatively short. However, the resultant films are mainly of a domain structure due to no film-forming anisotropy, and single-crystal films are hardly obtainable.
On the other hand, magnetic heads are utilized for recording-regenerating information in magnetic recording devices. However, the sites of magnetic heads are typically difficult to be adjusted so as to make the magnetic head trace the track-center correctly (tracking); namely, not only patterned media with anodized alumina pores but also the other patterned media currently suffer from non-appropriate tracking methods, thus easy and efficient arrangements of magnetic materials have been demanded for easily carrying out tracking.
The objects of the present invention are to provide nanohole structures applied to various fields such as magnetic recording media, DNA chips, and catalyst carriers, and methods for economically and efficiently producing the nanohole structures; stampers properly utilized to produce the nanohole structures and capable of producing the nanohole structures efficiently, and methods for producing the stampers; magnetic recording media adapted to hard disks utilized in various products such as external memory devices of computers and recording devices of public videos, capable of easy tracking, and allowing high-density recording, high-speed recording, and higher capacity without increasing the write-current at magnetic heads, and methods economically and efficiently for producing the magnetic recording media; and magnetic recording devices and a magnetic recording methods that utilize the magnetic recording media in perpendicular recording manner.